There are various situations where it is desirable to extrude a precise amount of food or to extrude a steady flow of food, eg. when making cookies where it is desirable that each cookie be of approximately the same size or where one wishes to control the flow of icing onto a cake.
There are various devices available in the market which deliver a measured amount of biscuit or cookie paste or dough to a baking tray prior to cooking. Such devices all work on the principle of what might be called a pistol-grip, operation of which causes a pawl to engage and disengage the teeth of a piston rod to permit the piston to advance a predetermined distance along the barrel to deliver a predetermined amount of paste-like food through an outlet.
The disadvantages of such devices is that the amount of paste-like food delivered through the outlet is predetermined by the size of the teeth on the piston rod and cannot be varied to suit the wishes of the user.